/Engine/Source/Runtime/AudioCaptureImplementations/AudioCaptureRtAudio/Public/RtAudioWrapper.h
FRtAudioInputWrapper wraps RtAudio implementation and provides a way to capture input audio from an hardware audio device.
typedef int(*)(void *OutputBuffer, void *InputBuffer, unsigned int NumFrames, double StreamTime, uint32 StreamStatus, void *UserData) FAudioCallback